This paper describes the preconcentration of the biomarker cardiac troponin I (cTnI) and a fluorescent protein (R-phycoerythrin) using cationic isotachophoresis (ITP) in a 3.9 cm long poly(methyl methacrylate) (PMMA) microfluidic chip. The microfluidic chip includes a channel with a 5× reduction in depth and a 10× reduction in width. Thus, the overall cross-sectional area decreases by 50× from inlet (anode) to outlet (cathode). The concentration is inversely proportional to the cross-sectional area so that as proteins migrate through the reductions, the concentrations increase proportionally. In addition, the proteins gain additional concentration by ITP. We observe that by performing ITP in a cross-sectional area reducing microfluidic chip we can attain concentration factors greater than 10 000. The starting concentration of cTnI was 2.3 μg mL−1 and the final concentration after ITP concentration in the microfluidic chip was 25.52 ± 1.25 mg mL−1. To the author’s knowledge this is the first attempt at concentrating the cardiac biomarker cTnI by ITP. This experimental approach could be coupled to an immunoassay based technique and has the potential to lower limits of detection, increase sensitivity, and quantify different isolated cTnI phosphorylation states.

Electromigration methods including CE and ITP are attractive for incorporation in microfluidic devices because they are relatively easily adaptable to miniaturization. After its popularity in the 1970s, ITP has made a comeback in microfluidic format (μ-ITP, micro-ITP) driven by the advantages of the steady-state boundary, the self-focusing effect, and the ability to aid in preconcentrating analytes in the sample while removing matrix components. In this review, we provide an overview of the developments in the area of μ-ITP in a context of the historic developments with a focus on recent developments in experimental and computational ITP and discuss possible future trends. The chip-ITP areas and topics discussed in this review and the corresponding sections include: PC simulations and modeling, analytical μ-ITP, preconcentration ITP, transient ITP, peak mode ITP, gradient elution ITP, and free-flow ITP, while the conclusions provide a critical summary and outlook. The review also contains experimental conditions for μ-ITP applications to real-world samples from over 50 original journal publications.

Lab-on-a-chip (LOC) technology provides a powerful platform for simultaneous separation, purification, and identification of low concentration multicomponent mixtures. As the characteristic dimension of LOC devices decreases down to the nanoscale, the possibility of containing an entire lab on a single chip is becoming a reality. This research examines one of the unique physical characteristics of nanochannels, in which native pH shifts occur. As a result of the electrical double layer taking up a significant portion of a 100 nm wide nanochannel, electroneutrality no longer exists in the channel causing a radial pH gradient. This work describes experimentally observed pH shifts as a function of ionic strength using the fluorescent pH indicator 5-(and-6)-carboxy SNARF®-1 and compares it to a model developed using Comsol Multiphysics. At low ionic strengths (~ 3 mM) the mean pH shift is approximately 1 pH unit whereas at high ionic strengths (~ 150 mM) the mean pH shift is reduced to 0.1 pH units. An independent analysis using fluorescein pH indicator is also presented supporting these findings. Two independent non-linear simulations coupling the Nernst-Planck equation describing transport in ionic solutions subjected to an electric field and Poisson's equation to describe the electric field as it relates to the charge distribution are solved using a finite element solver. In addition, the effects of chemical activities are considered in the simulations. The first numerical simulation is based on a surface ζ-potential which significantly underestimates the experimental results for most ionic strengths. A modified model assuming that SNARF and fluorescein molecules are able to diffuse into the hydrolyzed SiO 2 phase, and in the case of the SNARF molecule, able to bind to neutral regions of the SiO 2 phase agrees quantitatively with experimental results.

This paper describes the preconcentration of the biomarker cardiac troponin I (cTnI) and a fluorescent protein (R-phycoerythrin) using cationic isotachophoresis (ITP) in a 3.9 cm long poly(methyl methacrylate) (PMMA) microfluidic chip. The microfluidic chip includes a channel with a 5× reduction in depth and a 10× reduction in width. Thus, the overall cross-sectional area decreases by 50× from inlet (anode) to outlet (cathode). The concentration is inversely proportional to the cross-sectional area so that as proteins migrate through the reductions, the concentrations increase proportionally. In addition, the proteins gain additional concentration by ITP. We observe that by performing ITP in a cross-sectional area reducing microfluidic chip we can attain concentration factors greater than 10 000. The starting concentration of cTnI was 2.3 μg mL–1 and the final concentration after ITP concentration in the microfluidic chip was 25.52 ± 1.25 mg mL–1. To the author's knowledge this is the first attempt at concentrating the cardiac biomarker cTnI by ITP. This experimental approach could be coupled to an immunoassay based technique and has the potential to lower limits of detection, increase sensitivity, and quantify different isolated cTnI phosphorylation states.

Microfluidic devices provide ideal environments to study solvent extraction. When droplets form and generate plug flow down the microfluidic channel, the device acts as a microreactor in which the kinetics of chemical reactions and interfacial transfer can be examined. Here, we present a methodology that combines chemometric analysis with online micro-Raman spectroscopy to monitor biphasic extractions within a microfluidic device. Among the many benefits of microreactors is the ability to maintain small sample volumes, which is especially important when studying solvent extraction in harsh environments, such as in separations related to the nuclear fuel cycle. In solvent extraction, the efficiency of the process depends on complex formation and rates of transfer in biphasic systems. Thus, it is important to understand the kinetic parameters in an extraction system to maintain a high efficiency and effectivity of the process. This monitoring provided concentration measurements in both organic and aqueous plugs as they were pumped through the microfluidic channel. The biphasic system studied was comprised of HNO as the aqueous phase and 30% (v/v) tributyl phosphate in n-dodecane comprised the organic phase, which simulated the plutonium uranium reduction extraction (PUREX) process. Using pre-equilibrated solutions (post extraction), the validity of the technique and methodology is illustrated. Following this validation, solutions that were not equilibrated were examined and the kinetics of interfacial mass transfer within the biphasic system were established. Kinetic results of extraction were compared to kinetics already determined on a macro scale to prove the efficacy of the technique.